Inbox shared when it shouldn't be

An inbox for a user is shared though it shouldn't be. In the Web Interface, right clicking on Inbox, I show absolutely no reference to sharing. However, when using Zimbra Connector for Outlook, when that particular user's calendar is accessed, their Inbox is also visible using the TreeView in the mail tab.

Needless to say, their inbox and subfolders shouldn't be viewable... only their calendar. Any advice on how to correct this?